The Sega Mega Drive (released in North America as the Sega Genesis) wasn't a particularly popular machine in its home country, so Sega mostly focused on selling it to western gamers with a library that mostly consisted of aggressively-marketed action games, fighters and competitive sports titles. There were a few successful RPGs by Japanese studios - primarily Phantasy Star, Lunar and Shining Force - but the genre got much less attention on Genesis than it did on the SNES or even the PC Engine CD. Even the handful of western roleplaying properties that got Genesis adaptations - games like Might and Magic 2, Buck Rogers, Shadowrun and Eye of the Beholder - were all surprisingly respectable efforts for the platform. The result is that there aren't nearly as many RPGs to sort through, but it was also a challenge to find ones that can be considered truly bad.
Best: Phantasy Star IV: End of the Millennium (Sega, 1995)
Worst: Rings of Power (Naughty Dog, 1992)
An original effort by Naughty Dog (yes, that Naughty Dog), and a surprisingly ambitious one for an early 1990s game, attempting to create an Ultima-style "sim RPG" on the NES. A dynamic open world with hundreds of NPCs to talk to, lore to uncover, vehicles to board, numerous characters to recruit and an in-depth tactical combat system. The problem is that Ultima was intended for computers - platforms which had considerably higher RAM and graphics processing options and internal hard drives to store data, so they could pull it off; trying to do all of that on a console with 64 KB of RAM and VRAM and no internal storage was a much more daunting task. One they did a surprisingly admiral job with, but effort only gets you so far on such limited hardware - the game is very slow and choppy and it's easy to get lost with the extremely limited viewpoint you're afforded. It's also not immune to annoying old RPG trappings - you can stumble into a random fight with enemies well above your level and killed minutes into the game, and even later on when your party is well-equipped and trained you can still die pretty easily. Dungeons are pretty lengthy and monotonous corridors full of monsters and little else, and the loud and very twangy music gets grating pretty quickly. The eye for detail in its design and writing is laudable, but the Genesis's hardware simply wasn't cut out for this type of game.
Runner-up: Super Hydlide (T&E Soft, 1990)
As mentioned above, the Genesis was a pretty unpopular system in Japan, so it didn't get nearly as much attention from RPG developers making cheap licensed games and Dragon Quest knockoffs for an easy buck. Since RPGs were still a pretty niche genre in the west throughout the early '90s, it didn't get too many computer game ports either (and the handful it had were surprisingly pretty decent). So I had to come at it from a different angle and find a formative RPG that's aged like milk. Enter Super Hydlide, the third game in the Hydlide franchise and the first to get a 16-bit console port. While it is considerably more advanced than the very primitive 1984 original, with towns, NPCs, a day/night cycle, upgrading equipment and even a rudimentary Karma system that punishes you for harming "good" monsters, it still has many of the annoying trappings of its predecessors as well as '80s RPGs in general. First, you have to buy food and sleep regularly or your HP and attack power drop significantly. You also have to manage inventory weight; weapons and armor can only be equipped if your Strength is high enough, and you can't carry too much or you'll slow to a crawl. The game does away with the infamous "touch combat" of the original in favor of giving you a proper attack button, but combat is not particularly deep and you'll still have to do a lot of grinding in order to progress. Still, for all its irritations, I can't really hate it - there's enough of that outlandish '80s RPG fun to make it endearing. Start out in a fantasy world and somehow end up in space fighting an alien god with a lightsaber? That's just awesome any way you look at it. So, Super Hydlide is far from the worst RPG out there and has some fun with its outlandish elements, but the grindy nature and constant micromanagement of its design seriously hamper its enjoyability.